Pregnancy and childbirth are serious tests for any woman. And, in order to cope with it, the body mobilizes all its reserves. The main agents of such mobilization are special substances that cause all the cells of the body to work as a single system, performing certain tasks. The talk is about pregnancy hormones. How does the hormonal background change during pregnancy and how will these changes affect the well-being of the future mother?
Pregnancy Hormones and their Importance
Hormones are produced by numerous glands of internal secretion. In the human body, there are more than a hundred hormones known to science. However, their quantity is measured in micrograms (10-6) and nanograms (10-9). The role of pregnancy hormones is enormous: any minimal change in their level leads to a change in the work of millions of cells in the body.
It is thanks to hormones that we are capable of reproduction, maintaining pregnancy, and intrauterine development. During pregnancy, the level of some importance for the fetus hormones (thyroxine, cortisol) varies insignificantly.
The level of others (progesterone, prolactin) increases several times. In addition, there are hormones that appear in a healthy woman’s body only during pregnancy (chorionic gonadotropin, placental lactogen). The change in the balance of hormones during pregnancy triggers the process of birth and ensures its normal course and then recovery during the postpartum period.
Pregnancy Hormones: Chorionic Gonadotropin
The moment that triggers hormonal changes in the body is the introduction of the fetal egg into the wall of the uterus (implantation). During implantation, the cells of the fetal egg form villi, which connect to the blood vessels of the uterus, together forming a special organ – the chorion. Chorion also produces the first pregnancy hormone, which is called “human chorionic gonadotropin” (hCG).
HCG in the body of a healthy person is formed only during pregnancy. The simplest pharmacy test for pregnancy is based on the definition of HCG, excreted in the urine. The level of hCG directly depends on the development of the chorion, which means, from the gestation period: it increases twice every two days, reaching its peak at 8-10 weeks. After that, it begins to gradually decline, remaining practically at the same level during the second half of pregnancy. By the rate of growth of hCG in the blood in the first trimester, you can judge whether pregnancy and the fetus develop normally.
The appearance of these pregnancy hormones in the blood is a signal to the body that pregnancy has come and the whole metabolism needs to be restructured. HCG provides support for the vitality of the yellow body in the ovary, blocking the onset of the next menstruation. With the blood flow, hCG enters the main regulating center of the body – the pituitary gland. And the pituitary gland, having received such a signal, reconstructs all the hormonal activity of the body. Also, the adrenal glands react to the level of hCG in the blood, changing the synthesis of their hormones.
In addition, the level of hCG is important for the development of the chorion itself and its transformation into the placenta. In itself, the presence of hCG in the body is not felt by a woman, but it is this hormone that stimulates the production of female sex hormones (estrogens and progesterone), which cause changes in well-being.
Estrogens are a group of hormones, the main of which are estrone, estradiol, and estriol, produced predominantly in the ovaries. In the first 4 months of pregnancy, the main source of estrogens is the yellow body (a temporary organ that is formed every menstrual cycle in the ovary after ovulation at the site of the released follicle), and then the placenta. During pregnancy, the level of estrogen in a woman’s blood rises by 30 times.
Estrogens during pregnancy affect many important points of fetal development. For example, estrogens influence the rate of cell division in the early stages of embryo formation. Under their influence, the mammary glands get bigger in size and the milk ducts develop and grow, preparing for lactation. The woman’s breast swells and becomes more sensitive.
What’s more, estrogen’s pregnancy hormones can become the reason for headaches, dizziness, and insomnia. It is believed that estrogens give the future mother special femininity during pregnancy, she seems to blossom. However, they can also cause excessive skin pigmentation or hair loss.
Estrogens contribute to the increase in the size of the uterus. They also participate in the preparation of the body for childbirth. Estrogens increase the sensitivity of the uterine muscle to oxytocin (pituitary hormone, causing contractions) and soften the connective tissue of the cervix, facilitating its opening.
The level of estriol in the blood of a pregnant woman allows identifying abnormalities in the development of pregnancy. So, the decrease of this hormone is observed with some malformations of the fetus, intrauterine infection, and placental insufficiency.
Progesterone is a hormone that preserves pregnancy. Its main source in the early stages of pregnancy is the yellow body, and when after 12 weeks it disappears, its function is performed by the placenta. During pregnancy, the level of progesterone gradually increases. Its maximum level can be 20 times higher than the initial level.
Progesterone during pregnancy promotes stretching and relaxation of the uterine muscle, preventing premature termination of pregnancy. However, because of progesterone, pregnant women often suffer from nausea and heartburn. It reduces the tone of the ureters and bladder, which contributes to rapid urination and increases the risk of inflammation of the kidneys.
Progesterone reduces the tone of blood vessels, leading to fluid retention in the body, swelling, pressure drop, and varicose veins. In addition, progesterone affects the nervous system of the future mother. Because of progesterone, pregnant women feel drowsiness, irritability, and mood swings.
In the normal course of pregnancy, there is no need to monitor progesterone. But in women with the threat of miscarriage, the periodic tests allow the gynecologist to observe changes in the level of progesterone for the purpose of prognosis and correction of treatment. Medicines containing progesterone, take a leading place in the therapy of the threat of termination of pregnancy.
It is also one of those pregnancy hormones that stimulate the growth of the breast. Thanks to Chorionic Somatomammotrophin (as well as progesterone) the mammary gland grows in size. However, the action of this hormone can at the same time lead to an increase, for example, in the length of the foot (up to the change in the size of the shoes).
Growth Promoting Substances
The talk is about special substances produced by the placenta. They are stimulating the renewal of the body’s own tissues (e. g., connective tissue, and epithelium). Due to growth factors, the skin and connective tissue of the breast and abdomen are ready to meet the need for stretching.
Pregnancy Hormones of the Adrenal Glands
Mineralocorticoids and glucocorticoids. Their production (secretion) is stimulated by a specific hormone of the pituitary gland with the complex name “adrenocorticotropic hormone” (ACTH). An increase in the level of ACTH (and increase of adrenal hormones) is the body’s response to any stress. Pregnancy is also perceived as stress by the body.
ACTH itself contributes to the enhancement of skin pigmentation. Mineralocorticoids regulate water-salt metabolism, retaining salts and liquid in the body. Among the effects caused by them, we call the suppression of immunity (which prevents rejection of the fetus), hyperpigmentation of the skin, thinning of the hair, the formation of stretch marks – due to thinning of the skin, strengthening of hair growth on the body.
Placental Lactogen and Unconjugated Oestriol
Controlling the level of these hormones is extremely important for assessing the risk of developing hereditary chromosomal abnormalities in a future baby (Down’s, Edward’s, Turner, Patau syndrome, neural tube defect, etc.)
Unconjugated oestriol is produced by the placenta. This hormone improves the flow of blood through the vessels of the uterus, and also promotes the development of the ducts of the mammary glands, preparing the organism of the future mother for feeding the baby. The level of free oestriol varies because of many pathological conditions:
- fetoplacental insufficiency, when normal blood flow and nutrition in the placenta change;
- delayed development of the fetus;
- if you suspect a prolonged pregnancy.
Placental lactogen (PL) is also “produced” by the placenta. In the blood of a future mother, it can be detected already from the 5th week of pregnancy. Placental lactogen reaches its maximum value by 37-38 weeks. Then the level of these pregnancy hormones gradually decreases. However, the level of PL should be monitored throughout the gestation period.
First of all, it is necessary to assess the condition of the placenta and timely diagnose the placental insufficiency. A sharp decrease in the level of placental lactogen (more than 2 times) compared with the average level in accordance with the period of pregnancy may indicate a delay in the development of the fetus. In this case, it is necessary to take emergency measures to prevent a decrease in the level of PL by 80 % or more – this can lead to the death of the baby.
Thyroid Pregnancy Hormones
The normal functioning of the thyroid gland of the future mother plays a major role in the development of the baby.
Hormones of Motherhood
An irreplaceable role during the expectation of the baby is also played by the hormones of the pituitary gland (this is the endocrine gland located in the hypothalamic part of the brain). During labor, the pituitary gland releases oxytocin into the bloodstream, which stimulates uterine contractions. And after childbirth, an active synthesis of the hormone prolactin begins, which is responsible for lactation. With a lack of prolactin, a woman simply could not fully feed her baby with breast milk.
Relaxin is secreted in the ovaries and placenta during the late stages of pregnancy. It relaxes the cervix during labor, weakens the connection of the pubic symphysis to other pelvic bones. Thus, this hormone prepares the mother’s body for childbirth. In addition to this direct effect, relaxin promotes growth and the formation of new blood vessels, which reduces the risk of cardiovascular disease and increases the lifetime of women who have undergone pregnancy and childbirth.
The hormones listed above and the effect produced by them cannot be called complete. However, already on the basis of the given data, it becomes clear that hormones, which concentration in the blood rises during pregnancy, sometimes have the opposite effect. Ultimately, their influence on the appearance and health of women is not always pleasant. The degree of expression of “positive” and “negative” effects of pregnancy hormones depends on heredity, on the state of health of a woman at the time of conception, and on the characteristics of the course of a particular pregnancy.
Born in Belarus, 1985, a pedagogue and family psychologist, mother. Taking part in procedures of social adaptation of the foster children in new families. Since 2015 is a chief editor of the motherhow.com project, selecting the best and up-to-date material for those, who are planning, expecting, and already having babies.